I had 1GB OCZ DDR PC3200, CAS 2.5
My lowest Vista score was ram, at 4.5

I installed 2GB OCZ DDR PC3200 CAS 2.0 yesterday. (Though running at CAS 2.5)
My ram score went from 4.5 to 5.9.

Now, my lowest base score is my CPU:
AMD 4800+ X2 (running a tiny bit over @ 2.53GHz)
Score: 4.9

All my other scores are 5.8 or 5.9.

Video is Nforce 7800GTX 256MB
Hard drive is dual 250GB SATA2 in Nforce RAID stripe.

I will not be upgrading my CPU, as the absolute fastest socket 939 cpu available is Opteron 185, (2.6GHz)
$300+ for .1-.2 faster cpu is not worth it by any stretch of the imagination.